1. Field of the Invention
The present invention relates generally to methods for fabricating magnetic sensor elements. More particularly, the present invention relates to methods for fabricating soft adjacent layer (SAL) magnetoresistive (MR) sensor elements.
2. Description of the Related Art
The recent and continuing advances in computer and information technology have been made possible not only by the correlating advances in the functionality, reliability and speed of semiconductor integrated circuits, but also by the correlating advances in the storage density and reliability of direct access storage devices (DASDs) employed in digitally encoded magnetic data storage and retrieval.
Storage density of direct access storage devices (DASDs) is typically measured as areal storage density of a magnetic data storage medium formed upon a rotating magnetic data storage disk within a direct access storage device (DASD) magnetic data storage enclosure. The areal storage density of the magnetic data storage medium is defined largely by the track width, the track spacing and the linear magnetic domain density within the magnetic data storage medium. The track width, the track spacing and the linear magnetic domain density within the magnetic data storage medium are in turn determined by several principal factors, including but not limited to: (1) the magnetic read-write characteristics of a magnetic read-write head employed in reading and writing digitally encoded magnetic data from and into the magnetic data storage medium; (2) the magnetic domain characteristics of the magnetic data storage medium; and (3) the separation distance of the magnetic read-write head from the magnetic data storage medium.
With regard to the magnetic read-write characteristics of magnetic read-write heads employed in reading and writing digitally encoded magnetic data from and into a magnetic data storage medium, it is known in the art of magnetic read-write head fabrication that magnetoresistive (MR) read-write heads are generally superior to other types of magnetic read-write heads when employed in retrieving digitally encoded magnetic data from a magnetic data storage medium. In that regard, magnetoresistive (MR) read-write heads are generally regarded as superior since magnetoresistive (MR) read-write heads are known in the art to provide high output digital read signal amplitudes, with good linear resolution, independent of the relative velocity of a magnetic data storage medium with respect to a magnetoresistive (MR) read-write head.
In order to optimize signal amplitude and performance of a magnetoresistive (MR) read-write head, it is known in the art of magnetoresistive (MR) read-write head fabrication to employ at least either: (1) a longitudinal magnetic biasing to a magnetoresistive (MR) layer within a magnetoresistive (MR) sensor element within the magnetoresistive (MR) read-write head (in order to provide noise free operation of the magnetoresistive (MR) sensor element); or (2) a transverse magnetic biasing to the magnetoresistive (MR) layer within the magnetoresistive (MR) sensor element within the magnetoresistive (MR) read-write head (in order to provide a linear response of the magnetoresistive (MR) sensor element). Longitudinal magnetic biasing is typically provided employing either: (1) antiferromagnetic coupling of patterned antiferromagnetic material layers contacting opposite ends of the magnetoresistive (MR) layer within the magnetoresistive (MR) sensor element; or (2) permanent magnetic coupling of patterned permanent magnetic layers contacting opposite ends of the magnetoresistive (MR) layer within the magnetoresistive (MR) sensor element, while transverse magnetic biasing is typically provided through forming either in contact with or separated from the magnetoresistive (MR) layer by a conductor spacer layer a soft adjacent layer (SAL) of soft magnetic material, typically at least substantially co-extensive with the magnetoresistive (MR) layer within the magnetoresistive (MR) sensor element.
While transverse magnetically biased soft adjacent layer (SAL) magnetoresistive (MR) sensor elements provide generally enhanced linearity and performance with respect to otherwise equivalent magnetoresistive (MR) sensor elements absent soft adjacent layer (SAL) transverse magnetic biasing, soft adjacent layer (SAL) magnetoresistive MR) sensor elements are not formed entirely without problems. In particular, soft adjacent layer (SAL) magnetoresistive (MR) sensor elements when conventionally fabricated with a conductor spacer layer or soft adjacent layer (SAL) contacting a magnetoresistive (MR) layer within the soft adjacent layer (SAL) magnetoresistive (MR) sensor element suffer from problems including but not limited to: (1) current shunting through either one or both of the conductor spacer layer and the soft adjacent layer (SAL) (which leads to reduced signal amplitude of the magnetoresistive (MR) sensor element); and (2) thermal annealing induced elemental interdiffusion of the conductor spacer layer or the soft adjacent layer (SAL) with the magnetoresistive (MR) layer (which similarly also leads to reduced signal amplitude of the magnetoresistive (MR) sensor element). Similarly, soft adjacent layer (SAL) magnetoresistive (MR) sensor elements as conventionally fabricated do not necessarily always provide for optimal transverse magnetic biasing between a soft adjacent layer (SAL) and a magnetoresistive (MR) layer. It is thus towards the goal of fabricating soft adjacent layer (SAL) magnetoresistive (MR) sensor elements which simultaneously avoid: (1) current shunting into conductor spacer layers or soft adjacent layers (SALs) contacting magnetoresistive (MR) layers within the soft adjacent layer (SAL) magnetoresistive (MR) sensor elements; and (2) thermal annealing induced elemental interdiffusion of conductor spacer layers or soft adjacent layers (SALs) contacting magnetoresistive (MR) layers within those soft adjacent layer (SAL) magnetoresistive (MR) sensor elements, while providing enhanced transverse magnetic biasing between a soft adjacent layer (SAL) and a magnetoresistive (MR) layer within the soft adjacent layer (SAL) magnetoresistive (MR) sensor element, that the present invention is directed.
Various soft adjacent layer (SAL) magnetoresistive (MR) sensor elements have been disclosed in the art of magnetoresistive (MR) sensor element fabrication.
For example, Gill et al., in U.S. Pat. No. 5,508,866, discloses a soft adjacent layer (SAL) magnetoresistive (MR) sensor element comprising an exchange coupled antiferromagnetic bias layer contacting a soft adjacent layer (SAL) within the soft adjacent layer (SAL) magnetoresistive (MR) sensor element. The exchange coupled antiferromagnetic bias layer assures that the soft adjacent layer is fully saturated in a preferred direction.
In addition, Batra, in U.S. Pat. No. 5,483,402, discloses a soft adjacent layer (SAL) magnetoresistive (MR) sensor element having electrical leads whose planar surfaces are canted with respect to the easy axis of magnetization of a magnetoresistive (MR) layer within the soft adjacent layer (SAL) magnetoresistive (MR) sensor element. The soft adjacent layer (SAL) magnetoresistive (MR) sensor element so formed has a more symmetrical off-track performance profile which minimizes differences between the physical center of the soft adjacent layer (SAL) magnetoresistive (MR) sensor element and the magnetic center of the soft adjacent layer (SAL) magnetoresistive (MR) sensor element.
Further, Nix et al., in U.S. Pat. No. 5,573,809 disclose a soft adjacent layer (SAL) magnetoresistive (MR) sensor element comprising a magnetoresistive (MR) layer having a permanent magnet layer formed at each of its ends, where the magnetoresistive (MR) layer and the permanent magnet layers are separated by a tantalum or titanium spacer layer from a soft adjacent layer (SAL) within the soft adjacent layer (SAL) magnetoresistive sensor element. The soft adjacent layer (SAL) magnetoresistive (MR) sensor element so formed has a natural magnetic flux closure design.
Finally, Gill, in U.S. Pat. No. 5,715,120, discloses a soft adjacent layer (SAL) magnetoresistive (MR) sensor element employing a dielectric spacer layer separating a soft adjacent layer (SAL) from a magnetoresistive (MR) layer within the soft adjacent layer (SAL) magnetoresistive (MR) sensor element, where the soft adjacent layer (SAL) is further biased with an antiferromagnetic material layer contacting a surface of the soft adjacent layer (SAL) opposite the dielectric layer. The soft adjacent layer (SAL) magnetoresistive (MR) sensor element so formed exhibits an improved magnetoresistive (MR) effect due to attenuated magnetoresistive (MR) sense current losses into the soft adjacent layer (SAL).
Desirable in the art of soft adjacent layer (SAL) magnetoresistive (MR) sensor element fabrication are additional soft adjacent layer (SAL) magnetoresistive (MR) sensor elements which avoid: (1) signal amplitude degradation due to current shunting of conductor spacer layers or soft adjacent layers (SALs) contacting magnetoresistive (MR) layers within those soft adjacent layer (SAL) magnetoresistive (MR) sensor elements; and (2) signal amplitude degradation due to thermal annealing induced elemental interdiffusion of magnetoresistive (MR) layers with conductor spacer layers or soft adjacent layers (SALs) contacting those magnetoresistive (MR) layers within those soft adjacent layer (SAL) magnetoresistive (MR) sensor elements, while providing enhanced transverse magnetic biasing between a soft adjacent layer (SAL) and a magnetoresistive (MR) layer within the soft adjacent layer (SAL) magnetoresistive (MR) sensor elements. More desirable in the art are soft adjacent layer (SAL) magnetoresistive (MR) sensor elements which realize the foregoing objects while simultaneously being readily manufacturable. It is towards the foregoing goals that the present invention is more specifically directed.